This invention relates to rubber compouding and, more specifically, to the compounding of rubber which is to be bonded to reinforcing substrates. As is well known, the chemical make-up of reinforced rubber compounds is complex, and the demand for performance over widely varying conditions of stress and temperature has caused an increase in the variety of reinforcing substrates being used. Substrates such as polyester, nylon and steel are commonly used to reinforce rubber in the manufacture of pneumatic tires, pressure hoses and the like. It is well known to incorporate certain methylene donors and acceptors in the rubber compound in order to increase the bond between the rubber and the reinforcing substrates. It is also well known that some of the methylene donor-acceptor additions result in degradation of certain reinforcing substrates. For example, in the Endter et al U.S. Pat. No. 3,638,703, dated Feb. 1, 1972, reference is made to the degradation of polyester cord at high temperatures where hexamethylenetetramine is used as a methylene donor with resorcinol being used as a methylene acceptor. To reduce such degradation of polyester cord hexamethylenetetramine was first reacted with certain acids, and then the reaction products were used as methylene donors in the well-known donor-acceptor relationship. The use of resorcinol as an acceptor has not been entirely satisfactory since it must be added to the rubber compound at an elevated temperature, and at this temperature, resorcinol fumes, thereby liberating vapors which are noxious to persons working nearby. To reduce such problems, resorcinol has been prereacted to form the well known resorcinol-formaldehyde (RF) resins which have been used in place of resorcinol as methylene acceptors. However, the use of hexamethylenetetramine as a donor with a RF resin used as an acceptor has not been satisfactory because the adhesion thus obtained between the rubber and the substrate is poor. Accordingly, a search for satisfactory donors for use with RF resins has been conducted for several years. So far as we are aware, the only donor known to be satisfactory for use with RF resins is hexamethoxymethylmelamine which retards the rate of cure of the rubber compound in which the hexamethoxymethylmelamine was incorporated.